NU PUP (Nu Puppis). There are so many bright and beautiful stars
within the three parts of Argo (Puppis, Vela, and Carina) that the ones that would make a hit
in lesser constellations hardly stand out
at all. Mid-third magnitude (3.17) Nu Puppis (of no proper name)
recommends itself by being the western-most within the classical
outline of its constellation, by being in an interesting and fast
stage of evolution, and by falling into an arcane and rather weird
sub-class. At a distance of 423 light years, this class B (B8)
giant, with a measured temperature of 12,000 Kelvin, shines with a
luminosity (after allowance for ultraviolet radiation) of 1340
times that of the Sun, which yields a radius
8.5 times solar. Like many of its class, the star is a fast
rotator, spinning with an equatorial speed of at least 246
kilometers per second, which gives a rotation period under 1.7
days. The theory of stellar structure and evolution then tell of
a hefty five solar mass star that started at class B2. Now around
95 million years old, it gave up its core hydrogen fusion only a
few hundred thousand years ago (if that). It is now expanding and
cooling at its surface in preparation for brightening as a true red
giant only a few million years
hence, when it will become many times more luminous. There is some
evidence for variability of a couple hundredths of a magnitude over
a period of 6.5 days, which would make it an extreme form of
"slowly pulsating B star" (like 53
Persei), though it has not actually been so classified. Many
fast rotators are "B-emission" (or "Be") stars with circumstellar
disks that are related to the spin: Gamma
Cassiopeiae and Zeta Tauri come to
mind along with many others. While no classic emission has ever
been seen, Nu Pup is still called as a "shell star" (with its disk
seen edge-on) of a special sort. For all the collectors of arcana,
it is one of six "central quasi-emission peak" stars (which have
their emissions at wavelengths that fall in the middle of the
absorptions rather than to the sides, as is normal), if nothing
else showing how odd stellar classification can get. It has,
however, been observed in that state but once. It may be on its
way to becoming a real "Be" star. Or maybe it was once. But then
again, maybe not. We really do not know.